1. Field of the Invention
This invention relates to methods and materials for making porous resin-rigidified shaped articles from non-woven fabrics including filters, surgical trays, and the like.
2. Brief Description of the Prior Art
Various methods for making resin rigidified shaped articles are well known. Typical processes of this type involve precutting a piece of fabric and mounting it in a suitable pin frame; heat softening the fabric and molding it into the desired shape, coating the shaped article with a thermosetting or thermoplastic resin; and curing the resin to increase the rigidity of the shaped article.
For example, U.S. Pat. No. 2,576,864 discloses a method for manufacturing self-supporting mechanically strong filter elements which involves molding a thermosetting or thermoplastic resin-impregnated sheets of cellulosic multi-ply pad or batting, into a desired shape with heat and pressure causing the resin to cure. The cured resin rigidifies the filter element, that is, makes it a mechanically strong self-supporting structure. The word rigidified and related terms as used herein are intended to mean sufficiently stiffened to retain a desired (molded) shape without significant deformation under ordinary conditions of use. Similar processes are disclosed in U.S. Pat. Nos. 2,607,494; 3,972,694; and 3,256,372. U.S. Pat. Nos. 3,390,429 and No. 3,463,689 teach similar hollow cylindrical filter forming methods that include impregnating non-woven fibrous material with thermosetting resin; drying the resin at temperatures below the curve point; forming the filter on a rotating arbour and curing the resin.
The above described processes often involve the use of materials that produce noxious fumes during the curing steps, e.g. melamine/formaldehyde resins. Another disadvantage of the prior art processes is that they call for uninterrupted processing of the resin-impregnated shaped material until completion of the curing step to avoid undesirable deformations due to physical stresses on the article before it is sufficiently rigidified by curing. Performing all these steps in a single operation is often labor intensive and slow. Moreover, these processes must be capable of producing complex molded shapes, of suitable colors, at reasonable costs.
In some applications the resin rigidified shaped articles will require special properties, for example, in one contemplated application, as the shaped article is an enclosure for surgical devices that may be treated by sterilization techniques such as autoclaving or the like, such enclosures must permit the free flow of steam therethrough to effectuate sterilization of the enclosed device while retaining its rigidity. In another application, preparing self-supporting or shape retaining filter elements the resin rigidified materials may be required to have uniform thickness, density or porosity over at least a portion of the element's body.